Apparently there is a game out there called 'punch-for-punch'. A two person game, it involves player one hitting player two in the arm. Player two then returns the hit, trying for the exact same amount of force that player one hit them with. Usually it's done in the same spot. After a few rounds, the one who can't take it anymore 'gives', and becomes the loser. The loser gets nothing. The winner gets nothing. But a lot of pain is inflicted in a short amount of time, so I suppose the game is efficient, at least.

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It is not a great way to vent frustrations, however, since both players leave the game with smouldering resentment. Each one thinks that the other player hit them with more force than they used during their hit, thereby 'cheating'. Each player thinks that that they, on the other hand, played by the rules, only punching with as much force as they felt on the last hit. They're right that the other person used more force, but they're wrong in thinking that they did not. The average person is wired to be hypocritical.

Scientists automated the game in a lab, allowing people to hit each other with robotic arms that measured and recorded the exact amount of force used. The, presumably well-paid, volunteers swore that they directed the arms to use only the same amount of force that they had felt during the last blow. They were sure that their partners had increased the amount of force on each turn - some believing that their partners were 'plants' or had received special instructions from the researchers. The machines told a different story, showing that each blow was successively greater than the last.

The subjects even hit with greater and greater force when they were asked to smack themselves instead of their partners. The machine issued the first hit, and the people - knowing that they would only hit themselves - pushed back harder.

Scientists believed that this seemingly biological hypocrisy was served a practical function; it allowed people to distinguish the feel of the motions of their own body from the feel of outside forces acting on them. Many a person has absentmindedly chewed their lip too hard, or driven their nails into their palms during moments of tension. That won't do much damage, and shouldn't be a distraction. If someone else is driving their nails into a person's skin; that person needs to feel it keenly and immediately.

But how to test this? Scientists came up with two methods.

The first involved playing the robot-assisted-punch-for-punch game exclusively with schizophrenics. Many people with schizophrenia believe that certain phenomena generated by their own minds are the actions of someone or something else. They may hear voices, or believe that other people are forcing them to think certain things. Scientists believed that the blurring of the line between self and others may, paradoxically, allow schizophrenics to more accurately evaluate the force being applied to them and the force that they are applying to someone else. As it turns out, the scientists were correct. People with schizophrenia were more able to match the push of machines.

The second experiment consisted of a group of people without any specific diagnoses. The participated in the same game as the earlier group of people with schizophrenia - the robot pushing first and the person pushing back on themselves - and then were given a questionnaire to assess delusional behavior. Those who answered questions in a way that indicated delusional behavior were able to more accurately match the force of their own blow to the one doled out by the machine.